The rapid increase in vehicle traffic on roads and the associated traffic jams and prolonging of travel times are giving rise throughout the world to increased efforts to detect traffic states and to take them into account in the selection of a route and/or in the calculation of routes in navigation systems.
Digital maps are usually already out of date when they are supplied. It is therefore absolutely necessary to update the map if the digital map is to correspond to the current conditions. However, these updates comprise a large quantity of data since the entire map always has to be updated.
When there is a hazard warning on the basis of DSRC (Dedicated Short Range Communication), a warning is given about hazards on the piece of road in front of the vehicle which have been previously discovered by another vehicle or in some other way. In this context, the hazard warnings are passed on from vehicle to vehicle or transferred to vehicles via infrastructure.
Furthermore, it is known that vehicles transmit what is referred to as floating car data (FCD). The system which is used for this is composed of a GPS (Global Positioning System) receiver and a GSM (Global System for Mobile Communication) or GPRS module. Both modules are already present in many vehicles even without FCD functionality. The GPS receiver measures the position and the FCD methods determine travel times of the vehicle from a large amount of these position data. In the GSM network, these travel times are transferred as a chain of pearls, in which individual points of the piece of road are provided with location coordinates and time stamps, to the traffic data control center. The latter can then draw conclusions about the traffic situation from these travel times. This is the way in which traffic state data are acquired for traffic information services.